A liquid crystal display panel is a key component for a liquid crystal display. Generally, the liquid crystal display panel is formed by adhering a sheet of thin film transistor (TFT) array substrate to a sheet of color filter (CF) substrate and then dropping in liquid crystals between the two substrates.
A blue phase (BP) liquid crystal is a phase state having special characteristics in liquid crystals. The blue phase liquid crystal can transform isotropic refractive index into anisotropic refractive index in accordance with the voltage applied, and the liquid crystal display panel employing the blue phase liquid crystals can substantially improve its response speed without alignment process.
The conventional liquid crystal display panel employing the blue phase liquid crystals is still limited to the use of transverse electric field, i.e. the two electrodes generating the transverse electric field are formed on the same substrate of the liquid crystal display panel since the current blue phase liquid crystals are all positive liquid crystals. For example, with respect to an In-Plane Switching (IPS) type blue phase liquid crystal display panel, the blue phase liquid crystals are activated in the direction parallel to the plane where the substrate is located.
FIGS. 1 and 2 disclose a conventional IPS type blue phase liquid crystal panel. As shown in FIGS. 1 and 2, the conventional IPS type blue phase liquid crystal panel 200 comprises an array substrate 21, an opposite substrate 22 and a blue phase liquid crystal layer consisting of blue phase liquid crystals 23 sandwiched between the array substrate 21 and the opposite substrate 22. Pixel electrodes 211 and common electrodes 212 are alternately arranged on the array substrate 21. A lower polarizer 25 is provided on one side of the array substrate 21 far away from the blue phase liquid crystal layer and an upper polarizer 26 is provided on one side of the opposite substrate 22 far away from the blue phase liquid crystal layer, and moreover, the absorption axes of the lower polarizer 25 and the upper polarizer 26 are orthogonal.
FIG. 1 is a partially sectional schematic view of the conventional IPS type blue phase liquid crystal display panel in OFF state. As shown in FIG. 1, there is no voltage between the pixel electrode 211 and the common electrode 212 located on the array substrate 21 and further no transverse electric filed is generated therebetween when the IPS type blue phase liquid crystal display panel is in OFF state, and therefore the blue phase liquid crystals 23 remain spheroidal in OFF state. When light emitted from a backlight source (not shown) enters from the side of the array substrate 21 on the IPS type blue phase liquid crystal display panel 200, after passing through the lower polarizer 25, only the light whose polarization state is perpendicular to the absorption axis of the lower polarizer 25 can pass through, and because the spheroidal blue phase liquid crystals 23 at this time maintain isotropic refractive index, the light will not shift its polarization state after passing through the blue phase liquid crystals 23, and is then transmitted to the upper polarizer 26 through the opposite substrate 22. Since the absorption axes of the lower polarizer 25 and the upper polarizer 26 are orthogonally configured, the light after passing through the upper polarizer 26 is fully absorbed, and no light may pass through the IPS type blue phase liquid crystal display panel 200. Transmittance of the IPS type blue phase liquid crystal display panel 200 is zero, thus presenting dark state.
FIG. 2 is a partially sectional schematic view of the conventional IPS type blue phase liquid crystal display panel 200 in ON state. As shown in FIG. 2, the pixel electrode 211 and the common electrode 212 which are located on the array substrate 21 are applied with different voltages respectively when the IPS type blue phase liquid crystal display panel 200 is in ON state, and therefore a transverse electric field E is generated between the pixel electrode 211 and the common electrode 212. At this time, the blue phase liquid crystals 23 located in the transverse electric field E will be “horizontally stretched” along the direction of electric field line under action of the transverse electric field E from original spheroidal shape to ellipsoidal shape, and transformed from isotropic refractive index to anisotropic refractive index. When the light whose polarization state is perpendicular to the absorption axis of the lower polarizer 25 passes through the blue phase liquid crystals 23, the light passing the blue phase liquid crystals 23 is twisted to shift its polarization state since the blue phase liquid crystals 23 at this time maintain anisotropic to refractive index, allowing the light passing through the blue phase liquid crystals 23 not to be perpendicular to the absorption axis of the upper polarizer 26, thus the light may transmit through the upper polarizer 26, and pass through the IPS type blue phase liquid crystal display panel 200. Transmittance of the IPS type blue phase liquid crystal display panel 200 is not zero, thus presenting bright state. It is possible to control light transmittance by the voltages applied to the pixel electrode 211 and the common electrode 212 since the refractive index of the blue phase liquid crystals 23 is dependent on the electric field applied thereto, thus realizing presentation of respective gray scales for the IPS type blue phase liquid crystal display panel 200.
However, since the transverse electric field E has an impact only on the blue phase liquid crystals 23 around the pixel electrode 211 and the common electrode 212, transmittance of the blue phase liquid crystal display panel 200 is relatively lower and the electric field generated is relatively weaker, a relatively larger driving voltage is generally required for the blue phase liquid crystal display panel 200 employing this transverse electric field E.
The reason why the vertical electric field is not suitable for the current liquid crystal display panel employing the blue phase liquid crystals is that the blue phase liquid crystals will be “stretched” in the vertical direction under action of the vertical electric field generated between the pixel electrode on the array substrate of the liquid crystal display panel and the common electrode on the opposite substrate after voltage is applied to the liquid crystal display panel, and there is no shift in phase position for the polarized light passing through the blue phase liquid crystals stretched in the vertical direction, with the polarization state of the polarized light passing through the blue phase liquid crystals being the same with that when no voltage is applied to the blue phase liquid crystal display panel, furthermore, the light emitted from the backlight source cannot pass through the liquid crystal display panel since the absorption axes of the upper and lower polarizers on the liquid crystal display panel are orthogonal, so that it is impossible to acquire the bright state for the liquid crystal display panel and therefore it cannot be realized for presentation of respective gray scales for the blue phase liquid crystal display panel only by such the vertical electric field.